Chapel Hill, N.C. — Local doctors are leading a push to recognize a serious leg injury that's hard to diagnose, but that can be fatal.

It's called compartment syndrome, and doctors at the University of North Carolina and Duke University developed a simple way to diagnose and treat it early.

One place compartment syndrome can hide is behind more obvious injuries in emergency situations. As paramedics bring a car-crash patient to a hospital emergency department, for example, some injuries are obvious, like bleeding or blunt trauma to the head.

The patient’s legs may look normal.

“It's not always obvious when you first look at the leg that it may go on to develop compartment syndrome,” said Dr. Laurence Katz, an emergency medicine specialist at UNC Hospitals in Chapel Hill.

In compartment syndrome, a leg may swell to the point where blood can't get through the vessels. The treatment is simple – but a person could lose the leg or even die if the problem isn’t recognized early.

“As the blood flow decreases, the limb gets bluer and bluer and bluer,” Katz explained. In a higher-resolution gray-scale image that doctors see, it is darker areas that concern them. Blood flow shows up white.

Katz demonstrated with a blood-pressure cuff, which can cut off circulation temporarily. As the tightens on the arm, the warm colors in the image vanish. Then the cuff loosens.

“And there you go, there's your temperature returning,” Katz said as the image lightened.

Compartment syndrome must be treated within six to eight hours of the injury that causes it. Once doctors can spot it, the treatment is a fasciotomy – simple incisions in the skin of the leg to relieve pressure.

“Once the pressure is relieved, then the blood flow can return to the leg and the leg can be saved,” Katz said. It also may save a life.

Infrared cameras are now small enough to fit onto a helmet. Firefighters use them to find people inside a smoke-filled building where regular visibility is very poor.